Throughout this application, various references are cited in parentheses to describe more fully the state of the art to which this invention pertains. The disclosures of these references are hereby incorporated by reference into the present disclosure.
During the past several years, researchers have developed and used different cell culture and tissue engineering techniques for the culture and production of various types of cellular implants. Such systems are described for example in U.S. Pat. Nos. 5,041,138, 5,842,477, 5,882,929, 5,891,455, 5,902,741, and 6,228,635. Bioreactor systems have also been developed for the culture of cells and cellular implants and are described for example in U.S. Pat. Nos. 5,688,687, 5,728,581, 5,827,729 and 6,121,042.
The aforementioned methods and systems generally employ conventional laboratory culturing techniques using standard culture equipment for cell seeding of selected cell populations onto scaffolds. As such, the generated implants simply comprise proliferated cell populations grown on a type of biopolymer support where any manipulation of the cellular environment is limited to endogenous cell production of cytokines present in any standard cell culture, and application of shear and/or physical stresses due to circulation of cell culture media and physical manipulation of the support onto which the cells are seeded. The systems do not address nor are they capable of generating a tissue implant that comprises proliferated and differentiated cells representative of developing tissues in vivo and further integrated within a selected scaffold that can be successfully integrated in vivo. Moreover, known methods and systems are not capable of multi-functionally carrying out all of the steps of biopsy tissue digestion to yield disassociated cells, subsequent cell seeding on a proliferation substrate, cell number expansion, controlled differentiation, tissue formation and production of a tissue implant within a single automated tissue engineering system. This is primarily because known culture systems are not sophisticated in that they are not capable of automatically evaluating and manipulating the changing environment surrounding the developing implant such that cells progressively proliferate and differentiate into a desired implant.
Furthermore, conventional culture methods and systems are labor intensive and suffer from the drawbacks of contamination and varying degrees of culturing success due to human error and lack of continual performance evaluation. Conventional culture systems require that most of the initial steps in the preparation of cells for seeding (i.e. tissue digestion, cell selection) is performed manually which is time consuming, unreliable in terms of the quality of the tissue produced, and prone to culture contamination problems. The systems are incapable of supporting the automated preparation of tissue engineered implants from primary or precursor cells due to inherent design limitations that restrict the cell and tissue culture process, the inability to adequately monitor and modify the environment to support tissue development, and the absence of techniques to enable the implementation of effective quality control measures.
Thus, there remains a real and unmet need for an improved system for in vitro and ex vivo tissue engineering that can consistently meet the operational requirements associated with the different steps in the development and production of tissue engineered implants. Of particular importance is the ability to create functional tissue constructs where the cells present are active, differentiated and already expressing extracellular matrix. This involves more than, and is strikingly different to, the simple simulation of the mature in vivo environment present at the host site. This is because the preparation of functional de novo tissue fundamentally requires that the cells progress through a series of developmental stages as part of an ex vivo sequence.
In order to address both clinical and research requirements, new devices, methods and systems have been developed that obviate several of the disadvantages and limitations of conventional ex vivo culturing techniques and systems.